The ATP synthetase of heart mitochondria is a multicomponent complex which functions in electron transport driven ATP synthesis and as an ATPase to drive ion transport or reverse electron transport. We have prepared an antibody to a portion of this complex (against F1ATPase, 5 subunits) which immunoprecipitates the total complex (F1ATPase plus a member sector, 12-16 subunits) from the mitochondrial inner membrane. We propose to establish firmly the subunit structure of the ATP synthetase by examining several different preparations of the enzyme including the immunoprecipitated enzyme. Once we know the subunit structure we plan to determine the arrangement of these subunits in the complex by doing labelling experiments and cross-linking studies. Labelling with membrane impermeable reagents(35S) diazobenzenesulfonate and (35 S) NAP taurine will be directed at determining which subunits are exposed and which are buried in the complex. Also, the experiments will be designed to find out which subunits are on the matrix side and which are on the cytoplasmic side of the mitochondrial inner membrane. Cross-linking experiments will be directed at determining the proximities of subunits one to another in the complex. Special attention will be paid to the arrangement of the DCCD binding proteolipid as this component of the ATP synthetase has been implicated in proton translocation.